Polypropylene Fractions Research Articles

The impact resistance and mechanical properties of fiber reinforced self-compacting concrete (SCC) containing nano-SiO2 and silica fume

In this study, an extensive study including an experimental and analytical approach describes the effects of presence 1% nano-SiO2 and 7% silica fume on the key mechanical properties (compressive, tensile and flexural strength) and impact resistance of such compositions with inclusion of different fibre volume fractions of Polypropylene (PP) (.25, .5, .75 and 1%) and water-to-cement ratios (.27, .34, .41). The experimental tests have been implemented on two hundred and seventy specimens. Experimental results indicated that using both silica fume and nano-SiO2 instead of cement into the plain self-compacting concrete (SCC) leads to improved impact resistance and mechanical properties. This improvement was higher in terms of impact resistance compared to mechanical properties. Moreover, it was observed that using nano-SiO2 particles consequences to reduce the wall effect between PP fibre and its surrounding matrix. Reduction of this effect enhanced the impact resistance and mechanical properties of fibre-reinforced SCC. Moreover, a statistical/ analytical study was carried out on the executed large experimental database and it was observed that the impact resistance and mechanical properties of specimens containing silica fume and nano-SiO2 follow a normal distribution. Furthermore, the highest rate of gaining the number of post initial crack blows to failure for the fibre-reinforced specimens registered for specimens with water-to-cement ratio of .41.

Staggered-electromagnetophoresis with a Split-flow System for the Separation of Microparticles by a Hollow Fiber-embedded PDMS Microchip.

A novel microchip separation system for microparticles based on electromagnetophoresis (EMP) was developed. In this system, focusing and separation of flowing microparticles in a microchannel could be performed by staggered-EMP by controlling the electric current applied to the channel locally combined with the split-flow system for fractionation of eluates. To apply the electric current through the flushing medium in the microchannel, a hollow fiber-embedded microchip with multiple electrodes was fabricated. The hollow fiber was made by a semi-permeable membrane and could separate small molecules. This microchip allowed us to apply the electric current to a part of the microchannel without any pressure control device because a main channel contacted with the subchannels that had electrodes through the semi-permeable membrane. Moreover, the separation using this microchip was combined with the split-flow system at two outlets to improve separation efficiency. Using this system, with the split-flow ratio of 10:1, 87% of 3 μm polystyrene (PS) latex particles were isolated from a mixture of 3 and 10 μm particles. Even the separation of 6 and 10 μm PS particles was achieved with about 77% recovery and 100% purity. In addition, by controlling the applied current, size fractionation of polypropylene (PP) particles was demonstrated. Moreover, biological particles such as pollens could be separated with high separation efficiency by this technique.

Influence of different types of polypropylene fibre on the mechanical properties of high-strength oil palm shell lightweight concrete

This study aims to investigate the use of various polypropylene (PP) fibres with different aspect ratio and geometry to enhance the mechanical properties of oil palm shell fibre-reinforced lightweight concrete. The volume fractions (Vf) of 0.25%, 0.375% and 0.5% were studied for each fibre. As various PP fibres were added into oil palm shell fibre reinforced concrete, the marginal density reduction was reported. The effectiveness of new types of PP fibres to increase the compressive strength at later ages was more pronounced than at early age. It is found that low volume fractions of polypropylene twisted bundle (PPTB) fibres are more effective in improving the flexural strength of OPS concrete compared to its splitting tensile strength. The average modulus of elasticity (E value) is obtained to be 13.4GPa for all mixes, which is higher than the values reported in previous studies. An increase in the percentage third load compressive strength of 0.5% PPTB fibre of up to 11% was reported. Hence, this new types of PP fibres is a promising alternative solution to compensate lower mechanical properties for lightweight concrete.

Electrically conductive polypropylene nanocomposites with negative permittivity at low carbon nanotube loading levels.

Polypropylene (PP)/carbon nanotubes (CNTs) nanocomposites were prepared by coating CNTs on the surface of gelated/swollen soft PP pellets. The electrical conductivity (σ) studies revealed a percolation threshold of only 0.3 wt %, and the electrical conductivity mechanism followed a 3-d variable range hopping (VRH) behavior. At lower processing temperature, the CNTs formed the network structure more easily, resulting in a higher σ. The fraction of γ-phase PP increased with increasing the pressing temperature. The CNTs at lower loading (0.1 wt %) served as nucleating sites and promoted the crystallization of PP. The CNTs favored the disentanglement of polymer chains and thus caused an even lower melt viscosity of nanocomposites than that of pure PP. The calculated optical band gap of CNTs was observed to increase with increasing the processing temperature, i.e., 1.55 eV for nanocomposites prepared at 120 °C and 1.70 eV prepared at 160 and 180 °C. Both the Drude model and interband transition phenomenon have been used for theoretical analysis of the real permittivity of the nanocomposites.

Improving microisotacticity of Ziegler–Natta catalyzed polypropylene by using triethylaluminum/triisobutylaluminum mixtures as cocatalyst

Propylene was polymerized with TiCl4/Di/MgCl2 catalyst and cocatalysts containing triethylaluminum (TEA) and triisobutylaluminum (TiBA) in the presence of Ph2Si(OMe)2 (external donor) and hydrogen. Chain structure of the formed polypropylene (PP) was characterized by temperature-rise elution fractionation (TREF) combined with DSC and 13C NMR analysis of the main fractions. Increasing the amount of TiBA in cocatalyst leads to decrease of isotactic index of PP, meanwhile the microisotacticity of the main TREF fractions of PP was enhanced. PP produced with the catalyst activated by a 50/50 TEA/TiBA mixture has the same content of highly isotactic chains as PP produced with the TEA activated catalyst, but main TREF fractions of the former has higher microisotacticity than the later. Fast alkyl exchanges in TEA/TiBA mixtures are found by 1H NMR analysis of the mixtures. By analyzing alkanes released from hydrolyzed catalysts that have been treated with the cocatalyst, alkylation power of TEA/TiBA mixture was found to decrease with increasing its TiBA content. The effects of TEA/TiBA mixture in propylene polymerization is explained by the weaker alkylation power and lower Lewis acidity of the mixed alkylaluminums than pure TEA. Decrease in the alkylation power leads to reduction of active centers with the highest stereospecificity, meanwhile decrease in Lewis acidity intensified the role of De in enhancing stereospecificity of different active centers. When the amount of TiBA in TEA/TiBA mixture falls in a suitable range, the later effect becomes dominant, and evident improvement in microisotacticity of PP can be achieved.

Fabrication and Characterization of Functional Fiber Based on Polymethacrylate/Polypropylene Alloy via in situ Compatibilization

A poly(butyl methacrylate) (PBMA)/polypropylene (PP) blended fiber was prepared via reactive extrusion and melt spinning based upon the mechanism of in situ compatibilization, and its capacity to absorb organic liquid, gel fraction and remaining ratio were investigated. In addition, the miscibility between PBMA and PP, crystallization behavior and morphology of the blended fiber were characterized. The results indicate the blended fiber can absorb a certain amount of liquid, such as toluene, chloroform, and trichloroethylene, etc., and its absorption capacity gradually weakens and even disappears with increasing the mass fraction of PP in the mixture of PBMA and PP. The results obtained by thermogravimetric (TG) analysis show the miscibility between PBMA and PP becomes better due to an increase of the interactions between two phases under the effect of in situ compatibilization reaction, and the blended fiber has relatively better thermal stability with an increase in the mass fraction of PP. X-ray diffraction (XRD) results demonstrate the additional amount of PP has a significant impact on its crystallization capacity for the blended fiber, along with in situ compatibilization reaction. The results observed via field emission scanning electron microscope (FESEM) reveal that PP can efficiently improve the spinnability of PBMA, and endow the blended fiber with a near-optimal morphology. However, in situ compatibilization reaction also has a marked influence on the surface and cross-section morphology of the blended fiber.

EFFECTS OF HYDROGEN ON ACTIVE CENTERS IN PROPYLENE POLYMERIZATION WITH SUPPORTED ZIEGLER-NATTA CATALYST

The kinetics of propylene polymerization with a TiCl4/ Di / MgCl2( Di = internal donor) supported Ziegler-Natta catalyst was studied by measuring the number of active centers using 2-thiophenecarbonyl chloride as quenching agent. Influences of hydrogen and alkoxysilane type external donors on the number of active centers and chain propagation rate constant( k p) were investigated. The number and k p value of three groups of active centers that produce atactic,medium-isotactic and isotactic polypropylene( PP) fractions were determined. The catalyst activity was found to significantly increase with the addition of hydrogen,which was a result of simultaneous increases in the number of active centers and k p value. The three groups of active centers response to hydrogen differently. Hydrogen caused lower degree of increase in the number of active centers that produce atactic PP than the other two groups of active centers,and caused the highest degree of increase in the k p value of active centers that produce medium-isotactic PP. The hydrogen response of the active centers was also influenced by external donor. Increasing the bulkiness of alkyl groups in alkoxysilane donors leads to decreased hydrogen sensitivity,meanwhile the stereo- and regio-selectivities were evidently improved,implying that there are close relations between the hydrogen effect and the stereo-and regio-selectivities of the catalyst.A mechanistic model was proposed to explain the hydrogen effect.

Experimental Study on Resistance of Hybrid Fiber Reinforced Concrete to Freezing and Thawing

Experiments were conducted to study the resistance of steel-polypropylene hybrid fiber reinforced concrete (HFRC) to freezing and tharwing. The mix proportions of concrete in strength grade CF40 were designed according to the superposition mix design method, where five mass contents of polypropylene fiber changing in range of 0.3~1.5kg/m3 with 0.3kg/m3 increment while the fraction of steel fiber by volume was constant as 1.0%, and four fractions of steel fiber by volume changing in range of 0.5~2.0% with 0.5% increment while the mass content of polypropylene fiber was kept as 0.9kg/m3. The results show that the steel-polypropylene hybrid fiber can significantly increase the resistance of HFRC to freezing and thawing, the losses of dynamic elasticity modulus and flexural strength of HFRC decrease with the increasing mass content of polypropylene fiber and fraction of steel fiber by volume, there is the coupling effect of enhancing on resistance of HFRC to freezing and thawing by hybrid fibers.

Interactions between Low-Density Polyethylene (LDPE) and Polypropylene (PP) during the Mild Cracking of Polyolefin Mixtures in a Closed-Batch Reactor

Thermal decomposition behaviors of neat polypropylene (PP) and low-density polyethylene (LDPE) and LDPE/PP mixture with different ratios (30/70, 50/50, 70/30) are studied under nonisothermal conditions in closed-batch reactors. The presence of a synergistic effect is observed for mixture samples with a PP composition of >= 30 wt %. Different proportions of PP in LDPE/PP mixtures give different interaction effects. The 70/30 LDPE/PP mixture starts to give viscosity-reducing effect and can degrade at lower temperature; the 50/50 LDPE/PP mixture gives higher gaseous products yield, specifically, more methane, ethane and propane; and the 30/70 LDPE/PP mixture makes more aromatics formed in the liquid products. The synergetic effect of LDPE and PP is related not only to the mass fraction of PP, but also to the reaction time. The interactions mechanism are related to enhanced intermolecular hydrogen transfer between LDPE/its cracked products and PP/its cracked products, not only in the liquid phase but also in the gas phase, because of the long cracking time in closed-batch reactors, where PP/its cracked products provide more radicals and PE/its cracked products provide more secondary hydrogen for intermolecular hydrogen transfer, and the combination of these factors enhances the chain breakage. This study also indicates that LDPE/PP mixture increases the aromatics formation mainly by increasing olefinic content due to the more beta-scission reactions in the LDPE/PP mixture mild cracking.

The optimal formulation of recycled polypropylene/rubberwood flour composites from experiments with mixture design

A mixture design was used in experiments, to determine the optimal mixture for composites of rubberwood flour (RWF) and reinforced recycled polypropylene (rPP). The mixed materials were extruded into panels. Effects were determined of the mixture components rPP, RWF, maleic anhydride-grafted polypropylene (MAPP), and ultraviolet (UV) stabilizer, on the mechanical properties. The overall composition significantly affected flexural, compressive, and tensile properties. The fractions of recycled polypropylene and rubberwood flour increased all the mechanical material properties; however, increasing one fraction must be balanced by decreasing the other, and the rubberwood flour fraction had a higher effect size. The fraction of MAPP was best kept in mid-range of the fractions tested, while the UV stabilizer fraction overall degraded the mechanical properties. Our results suggest that the fraction of UV stabilizer should be as small as possible to minimize its negative influences. The models fitted were used for optimization of a desirability score, substituting for the multiple objectives modeled. The optimal formulation found was 50.3wt% rPP, 44.5wt% RWF, 3.9wt% MAPP, 0.2wt% UV stabilizer, and 1.0wt% lubricant; the composite made with this formulation had good mechanical properties that closely matched the model predictions.

Mechanism of Propylene Polymerization with MgCl2-Supported Ziegler–Natta Catalysts Based on Counting of Active Centers: The Role of External Electron Donor

Four R1R2Si(OMe)2 type compounds were added as an external electron donor (De) in propylene polymerization with TiCl4/Di/MgCl2 type supported Ziegler–Natta catalysts (Di = internal donor). Each polypropylene (PP) sample was fractionated into three parts (atactic, medium-isotactic and isotactic PP), and the number of active centers ([C*]/[Ti]) in each PP fraction was counted using 2-thiophenecarbonyl chloride as the quenching and tagging agent. The gradual decrease of [C*]/[Ti] with De/Ti ratio is ascribed to competitive and reversible coordination of De on either central Ti of the active center or Mg adjacent to the central Ti. The former coordination leads to deactivation of C*, and the latter one leads to still living C*. The chain propagation rate constant (kp) of the active centers producing atactic, medium-isotactic and isotactic PP change with De/Ti in different ways. Only the kp of active centers producing isotactic PP was evidently increased by De. Enhancement in isotacticity of PP product is found to be a combined result of both deactivation of active centers by De and selective activation of the active centers that produce isotactic PP. Changing the alkyl groups of R1R2Si(OMe)2 leads to an altered balance between the deactivation and activation effects of De.

Investigation into Failure in Mining Wire Ropes—Effect of Crystallinity

A range of blends of polypropylene-polyethylene are investigated for their mechanical performances. These speciality polymer blends are chemically designed to suit high modulus/high load bearing mining wire rope applications subjected to continued bending and tensile stresses and fluctuating loads and are exposed to extreme weather conditions. In this paper we study the influence of different parameters on the performance of the wire ropes: chemistry of polymer, crystallinity of the polymer matrix, and the morphology. The FTIR and SEM studies revealed that the high fraction of polypropylene in polypropylene-polyethylene matrix lead to early failure as a result of incompatibility and phase segregation and high spherulite sizes of the polymer matrix.

Fabrication and characterization of oil-absorptive fiber by polypropylene and poly(butyl methacrylate-co-hydroxyethyl methacrylate) blends

A series of blend fibers based on a certain weight polypropylene (PP) and poly(butyl methacrylate- co-hydroxyethyl methacrylate) (PBMA- co-HEMA) were prepared via melt spinning in a corotating twin screw extruder. The morphology and structure of the blend fiber was studied by stereoscopic microscopy, polarized optical microscopy, wide-angle x-ray diffraction and field emission scanning electronic microscopy. Thermal properties were carried out by means of differential scanning calorimetry and melt flow index. The results demonstrated that the crystalline structure is proven to be greatly destroyed owing to the entanglement and cross-linking of molecular chains caused by hydrogen bond network of the copolymer in the blend. Oil absorbency decreases with increasing mass fraction of PP in the blend fiber. Moreover, the enthalpy of crystallization and supercooling temperature decrease as the content of PBMA- co-HEMA component increases.

Study on Crystallization Behavior of Liquid Crystalline Polyacrylates Induced Isotactic Polypropylene

A series of polypropylene (PP) blends were obtained by blending isotactic PP and different mass fraction of liquid crystalline polyacylates (LCP-A) at a proper process program. The effect of LCP-A as a new nucleator on crystallization behacior of isotactic PP has been investigated with wide angle X-ray diffraction (WAXD), polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The experimental results showed that LCP-A in the PP played a role in the heterogeneous nucleation effect, supplied much crystal nucleus, enhanced the crystallization velocity and temperature, and the spherulites became smaller and more homogeneous. Moreover, β-phase in the PP was induced. In addition, the relative content of β-crystal (Kβ) increased with increasing LCP-A content or crystallization temperature, reached a maximum value, and then decreased as the temperature or LCP-A content further increased. Kβ of PP with 0.8% LCP-A isothermally crystallized at 125°C for 1h was 21%. POM results that showed the morphology of β and α spherulite disappeared at 156°C and 172°C, respectively.

Property manipulated polypropylene–iron nanocomposites with maleic anhydride polypropylene

Magnetic polypropylene (PP) polymer nanocomposites (PNCs) were fabricated with the reinforcing core–shell Fe–Fe2O3 nanoparticles (NPs) synthesized by an in-situ thermal decomposition method. Maleic anhydride functionalized PP (M-PP) with two different molecular weights (Mn = 800, called LM-PP; Mn = 8000, called HM-PP) were found not only serving as surfactant to control the particle size, but also influencing the oxidation degree of the synthesized NPs. With regular PP only, the average nanoparticle size was 15.9 ± 2.2 nm. The NPs decreased to 10.6 ± 1.3 nm and 14.6 ± 2.7 nm in the presence of LM-PP and HM-PP, respectively. A surprisingly enhanced thermal stability by 117.6 °C in air was observed due to both the oxygen trapping effect of the NPs and the polymer–particle interaction. With only 2.4 wt% of M-PP in the PNCs, the complex viscosity was decreased by 86% at the frequency of 0.1 Hz. Enhanced saturated magnetization of the PNCs after introducing LM-PP indicated that the NPs were partially protected by the LM-PP shell and less dominated by the surface oxidation effects. The room temperature Mossbauer spectra analysis confirmed the oxidation degree of the NPs in each PNC and the molecular weight effect of M-PP on the restricted oxidation behavior of the NPs was studied as well. Both LM-PP and HM-PP change the crystalline fraction (Xc) of PP slightly (<1%) in the M-PP–PP blends. While in the PNCs, their contributions to the Xc of PP are significantly different from each other. Specifically, LM-PP increases the Xc of PP by 6.4% and HM-PP reduces the Xc by 10.1%. The electrical conductivity of these PNCs is also comparatively investigated.

Effect of carbon nanotubes on dynamic mechanical properties, TGA, and crystalline structure of polypropylene

AbstractThis paper is devoted to the preparation of thermoplastic nanocomposites of polypropylene (PP) and different amounts of single‐walled carbon nanotubes (SWNTs) in the range 0.25–2 wt %. The effect of SWNT content on the dynamic mechanical behavior, thermal degradation, crystalline structure, and the kinetic crystallizability of PP were studied. The results obtained from dynamic mechanical thermal analyzer (DMTA) showed that the maximum storage modulus was achieved when 1 wt % SWNT was added into the pristine polymer. Thermal stability of the nanocomposites was measured by thermogravimetric analyzer (TGA). From the TGA results, it was found that the weight fraction of PP which was located at the interface for the nanocomposite containing 0.5% SWNT was about 60%, and this value did not change much with the addition of higher amounts of SWNT. Moreover, the thickness of the interface between PP and SWNT was estimated to be of the order of 101 nm which is very close to the radii of gyration of PP molecular chains. Wide angle X‐ray diffractometer (WAXD) was used to explore the crystalline structure of water and slow‐cooled samples. It was found that the crystallization of PP in 040 lattice plane increased for the nanocomposites compared with PP for both cooling rates studied. It was also found that the kinetic crystallizability values were nearly the same for PP and the nanocomposites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Analytical modeling of strength in randomly oriented PP and PPTA short fiber reinforced gypsum composites

Fiber reinforced gypsum are prevalent building materials in which short fibers with high tensile strength are embedded into a gypsum matrix to produce supplemental strong and lightweight construction materials. Due to confrontation to a rising risk of death and economic disaster in earthquake-prone areas, quake-resistant materials and structures should be employed for building constructions. Gypsum based composites as a unique candidate for this purpose reduce the risks and produce much confident construction materials for residential buildings. In this work tensile strength of gypsum composites with different volume fraction of polypropylene (PP) and poly-paraphenylene terephthalamide (PPTA) fibers up to 15% were studied. Stress transfer ability from matrix to fibers were analyzed using theoretical shear lag analyses, scanning electron microscope, and pull out tests. The interfacial characteristics were also studied by scanning electron microscope (SEM). The ability of the composites to withstand against longitudinal tensile load was also studied by tensile tests of dog-bone shaped, random oriented fiber reinforced gypsum. Tensile strength of randomly oriented short fiber reinforced gypsum was evaluated by a mathematical model. The obtained results from the model and experimental results have been compared and discussed.

Toughness increase of self compacting concrete reinforced with polypropylene short fibers

Increases in bending tests by the addition of low volume fractions of Polypropylene (PP) Short Fibers PP. These toughness increases are similar to those attained by Fiber Reinforced Concrete (FRC) referred elsewhere as Engineered Cementitious Composites (ECC), having some ductility and strain hardening in direct tensile and flexural tests. Concretes mixtures were manufactured using natural pozzolanic blended Portland cement, volcanic crushed coarse aggregates and fine sand from Sahara desert dunes (0-1 mm) from Canary Islands quarries and sand reservoirs, respectively, besides ordinary siliceous sand (0-4 mm) and fly ash from an anthracite-coal heat generator.

Initiation of Cavitation of Polypropylene during Tensile Drawing

The effect of stabilizers, additives, and low molecular weight fractions on cavitation during tensile drawing was studied in polypropylene. The additives were extracted from compression molded samples by critical CO2 and also by a mixture of nonsolvents. The extract was an oily liquid composed of antioxidant, processing stabilizer, and a spectrum of low molecular weight fractions of polypropylene. Purified polypropylene exhibited surprisingly more intense cavitation than pristine polypropylene as it was determined by small-angle X-ray scattering and volume strain measurements. Intensification of the cavitation process in the purified samples was explained by the changes in the amorphous phase, namely, the changes in free volume by eliminating low fractions and soluble additives. An increase in free volume was probed with positron annihilation lifetime spectroscopy. Intense formation of cavitation pores in purified polypropylene proves that initiation of cavitation in polypropylene has a homogeneous nature.

γ-PHASE POLYPROPYLENE CRYSTALLITES INDUCED BY ORGANO-CLAY MODIFIED BY ALKYL PHOSPHONIUM IONS

The Organo-Clay was prepared by alkyl phosphonium ions treating of Na-montmorillonite.The X-ray diffraction(XRD) patterns of Na-Clay and Organo-Clay shows that the position of the(001) plane diffraction peak of the Na-Clay appears around 5.94°,corresponding to the interlayer distance(d) of 1.48 nm calculated from the Bragg law,and the position of the(001) plane diffraction peak of the Org-Clay appears around 4.99°,d = 1.78 nm.The result proves that the alkyl phosphonium are intercalated into the galleries of the clay layers.The polypropylene(PP)/Org-Clay nanocomposites were prepared by melt intercalation and XRD and transmission electron microscopy(TEM) both indicated that PP chains could be intercalated into the interlayer of the Org-Clay.The nanocomposites possess exfoliation structure and intercalation structure.The process of melting for PP/Org-Clay nanocomposites were studied with differential scanning calorimetry(DSC),and the result indicted that the addition of the Org-Clay had hardly effect on the degree of crystallization for PP.XRD results shows the position of the γ-PP(130) plane diffraction peak of the PP/Org-Clay nanocomposites appears around 19.8°and DSC heating cuvers of PP /Org-Clay nanocomposites at speed of 5 K/min revealed that the γ-PP melt peak of the PP/Org-Clay nanocomposites appearing around 149℃.It can inferred that the Org-Clay may promote the formation of γ-phase PP crystallites in the PP /Org-clay.When adding 5 wt% Org-Clay,the mass fraction of γ-phase PP is about 12%.